Loaded weight measurement method and loaded weight measurement device for dump truck

ABSTRACT

To measure the loaded weight of a dump truck, accurately and inexpensively. In a dump truck comprising a set of equalizer bars respectively provided rotatably on the left and right-hand sides of a vehicle body; first vehicle wheels supported respectively by way of first suspension devices on one side of each equalizer bar; second vehicle wheels supported respectively by way of second suspension devices on the other side of each equalizer bar; and third vehicle wheels provided respectively on the left and right-hand sides of the vehicle body separately from the equalizer bars, and being supported respectively by way of third suspension devices; a first load applied to the second suspension device is detected; a second load applied to the third suspension device is detected; the angle of inclination of the vehicle body is detected; and a loaded weight is calculated on the basis of the first and second loads, and the angle of inclination.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a loaded weight measurement method andloaded weight measurement device for a dump truck.

2. Description of the Related Art

A method is known in the prior art (Japanese Patent Laid-open No.61-34425) in which the weight of cargo is measured by detecting the loadapplied respectively to the front wheels and the rear wheels of a dumptruck and correcting these detected loads on the basis of the angle ofinclination of the vehicle and the center of gravity of the vehicle.

According to the prior art technology described in Japanese PatentLaid-open No. 61-34425, it is possible to determine the weight of acargo simply by detecting the loads applied respectively to the frontwheels and rear wheels. However, this conventional technology can onlybe applied to a dump truck having respective left and right-hand pairsof wheels in the front and rear portions of the vehicle body. Therefore,it is difficult to apply directly to a dump truck having two pairs ofwheels in either the front section or rear section, as in the case of anarticulated dump truck, for instance.

For example, in the case of an articulated dump truck, respective leftand right-hand pairs of front wheels, central wheels and rear wheels areprovided. The weight of an articulated dump truck is supported in adivided fashion by the front wheels, the central wheels and the rearwheels. Therefore, in order to measure the weight of cargo loaded intothe vessel of the truck accurately, it is necessary to measure therespective loads applied to the front wheels, central wheels and rearwheels.

Here, for example, if the front wheels and the rear wheels are supportedrespectively by suspension cylinders, and the central wheels aresupported by springs, then it is difficult to detect the load applied tothe central wheels, accurately. A method can be conceived in which theamount of compression of the springs supporting the central wheels ismeasured and the load is determined on the basis of this amount ofcompression. However, this method produces significant error in themeasurement of the loaded weight. The relationship between thecompression of the springs and the load varies due to the effectsfriction in the springs, and other factors.

Therefore, a method may be conceived in which the central wheels arealso supported by suspension cylinders, instead of springs, the loadapplied to the central wheels being measured by means of pressuresensors provided in these suspension cylinders. However, suspensioncylinders are expensive compared to springs, and since pressure sensorsmust also be provided, the manufacturing costs of the dump truckincrease.

The aforementioned problems are not limited to the case of articulateddump trucks, and are also common to dump trucks which have two pairs ofwheels supported on rotatable equalizer bars, in at least the front orrear portion of the vehicle body.

SUMMARY OF THE INVENTION

The present invention was devised with the foregoing problems in view,an object thereof being to provide a loaded weight measurement methodand a loaded weight measurement device for a dump truck whereby theloaded weight can be detected inexpensively and accurately, in a dumptruck having two pairs of wheels supported by equalizer bars provided ina rotatable fashion. Other objects of the present invention will becomeapparent from the following description of the embodiments.

In order to achieve the aforementioned objects, the loaded weightmeasurement method for a dump truck relating to the present invention isa loaded weight measurement method for a dump truck comprising a set ofequalizer bars respectively provided rotatably on the left andright-hand sides of a vehicle body; first vehicle wheels supportedrespectively by means of first suspension devices on one side of eachequalizer bar; second vehicle wheels supported respectively by means ofsecond suspension devices on the other side of each equalizer bar; andthird vehicle wheels provided respectively on the left and right-handsides of the vehicle body separately from the equalizer bars, and beingsupported respectively by means of third suspension devices, the loadedweight measurement method comprising: a first step of detecting a firstload applied to either the first suspension device or the secondsuspension device; a second step of detecting a second load applied tothe third suspension device; a third step of detecting the angle ofinclination of the vehicle body; and a fourth step of calculating aloaded weight on the basis of the first and second loads detectedrespectively in the first and second steps, and the angle of inclinationdetected in the third step.

A composition may be adopted wherein a judgment step for judging whetheror not the equalizer bars are in a state of free rotation is executedprior to the first step, respective steps following the first step areexecuted if it is judged in the judgment step that the equalizer barsare in a state of free rotation, and a notification is reported if it isjudged in the judgment step that the equalizer bars are not in a stateof free rotation.

A composition may be adopted wherein the judgment step judges whether ornot the equalizer bars are in a state of free rotation on the basis of adetection signal from abutment detecting means for detecting an abuttedstate of the equalizer bars and the vehicle body.

A composition may be adopted wherein the judgment step judges whether ornot the equalizer bars are in the state of free rotation, by comparingat least one of the first load detected in an empty state in the firststep and the loaded weight calculated in an empty state in the fourthstep, with a previously established prescribed value for an empty state.

The loaded weight measurement device for a dump truck according to afurther aspect of the present invention comprises: a first loaddetecting section for detecting a first load applied to either the firstsuspension device or the second suspension device, on the basis of adetection signal from first load detecting means provided in only one ofthe first suspension device and the second suspension device; a secondload detecting section for detecting a second load applied to a thirdsuspension device on the basis of a detection signal from second loaddetecting means provided in the third suspension device; a total loadcalculating section for calculating a total load applied to the firstand second suspension devices on the basis of the ratio between therespective distances from the center of rotation of the equalizer bar tothe first and second suspension devices, and the detected first load; avertical component calculating section for respectively calculating thevertical component of the calculated total load and the verticalcomponent of the detected second load, on the basis of a detectionsignal from inclination angle detecting means provided in the vehiclebody; and an overall load calculating section for calculating an overallload by adding the vertical component of the total load thus calculatedto the vertical component of the second load thus calculated.

According to the present invention, in a dump truck comprising firstvehicle wheels and second vehicle wheels which are coupled by equalizerbars, it is possible to calculate the loaded weight by using first andsecond load detecting means only, without provided load detecting meansin all of the suspension devices. Therefore, it is possible to detectthe loaded weight accurately by means of a small number of detectingmeans.

According to the present invention, it is possible to start measurementof the loaded weight after judging whether or not the equalizer bars arein a state of free rotation. Therefore, it is possible to measure theloaded weight after previously confirming that accurate measurement canbe achieved. If accurate measurement is not possible, then anotification to this effect is reported to the truck operator or loadingoperator, or the like, in order that suitable countermeasures can beadopted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a dump truck relating to an embodiment of thepresent invention;

FIG. 2 is a plan view showing an enlarged view of a rear frame;

FIG. 3 is a side view showing an enlargement of the vicinity of anequalizer bar;

FIG. 4 is a cross-sectional diagram of a suspension cylinder;

FIG. 5 is a block diagram showing the circuit structure of a controller;

FIG. 6 is a block diagram showing the functional composition of acontroller;

FIG. 7 is a flowchart showing a calibration process;

FIG. 8 is a flowchart illustrating a loaded weight measurement process;

FIG. 9 is a flowchart showing a work sequence of a dump truck relatingto a second embodiment;

FIG. 10 is a side view of a state where an equalizer bar is abuttedagainst a stopper;

FIG. 11 is a flowchart of a process for judging the suitability of avehicle position;

FIG. 12 is a side view of the vicinity of an equalizer bar relating to athird embodiment of the present invention;

FIG. 13 is a block diagram showing the circuit structure of acontroller; and

FIG. 14 is a flowchart of a process for judging whether or not anequalizer bar is abutted against a stopper.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, an embodiment of the present invention is described in detailwith reference to the drawings. As described below, the presentembodiment discloses a dump truck (11) having vehicle bodies (24, 25); avessel (21) provided on the vehicle body (25); a set of equalizer bars(30) respectively provided rotatably on the left and right-hand sides ofthe vehicle body (25); first vehicle wheels (18) supported respectivelyon one side of each equalizer bar (30) by means of a first suspensiondevice (31); second vehicle wheels (19) supported respectively on theother side of each equalizer bar (30) by means of a second suspensiondevice (16); and third vehicle wheels (17) provided respectively on theleft and right-hand sides of the vehicle body (24), separately from theequalizer bars (30), and supported respectively by means of a thirdsuspension device (14).

The dump truck (11) further comprises: first load detecting means (23,230) for detecting a first load acting on either the first suspensiondevice (31) or the second suspension device (16); second load detectingmeans (22, 220) for detecting a second load acting on the thirdsuspension device (14); inclination angle detecting means (20) fordetecting the angle of inclination of the vehicle body (25); controlmeans (47) for calculating the loaded weight of the vessel (21) on thebasis of the first and second loads and the angle of inclination; andoutputting means (48, 47B, 114) for outputting the loaded weightcalculated by the control means (47).

First Embodiment

A first embodiment of the present invention will be described withreference to FIG. 1–FIG. 8. FIG. 1 is a side view of an articulated typedump truck 11.

As shown in FIG. 1, the dump truck 11 comprises a front vehicle body 24disposed on the front side and a rear vehicle body 25 disposed on therear side. The front vehicle body 24 is supported by means of a frontframe 27 and the rear vehicle body 25 is supported by means of a rearframe 28. The rear frame 28 is coupled bendably and swingably withrespect to the front frame 27. An driver's cabin 36 is mounted on thefront frame 27.

A left and right-hand pair of steering cylinders 35, 35 are providedspanning between the front frame 27 and the rear frame 28. Byrespectively extending or contracting the steering cylinders 35, 35, therear frame 28 can be made to turn with respect to the front frame 27,and hence a steering operation can be performed.

A vessel 21 for loading a cargo, such as sand, for example, is providedon top of the rear frame 28. A pair of lift cylinders 26, 26 areprovided between the left and right-hand sides of the front portion ofthe vessel 21 and the rear frame 28. The lower rear portion of thevessel 21 is attached rotatably to the rear frame 28 by means of vesselpins 37. By extending or contracting the lift cylinders 26, 26, thevessel 21 is rotated upwards and downwards about the vessel pins 37. Theoperation of raising up the vessel 21 is called “tipping up”, and theoperation of lowering the vessel 21 is called “tipping down”. FIG. 1shows a state where the vessel 21 has been lowered and is seated on therear frame 28.

A front arm 12 which is V-shaped in plan view is provided rotatably onthe front frame 27. The front end portion 12A of the front arm 12(namely, the apex of the V shape) is supported on the lower portion ofthe front arm 27, rotatably in the vertical direction.

A pair of left and right-hand front wheels 17, 17 are installed on thetwo side faces of the rear end portion 12B of the front arm 12. Theserespective front wheels correspond to one example of “third vehiclewheels”. The upper portion of the rear end section 12B is supported onthe front frame 27 via a front suspension cylinder 14, which is oneexample of a “third suspension device”.

Here, FIG. 2 is a plan view of a rear frame 28 showing a state where thevessel 21 has been removed. As illustrated in FIG. 1 and FIG. 2, theleft and right-hand pair of equalizer bars 30, 30 are provided rotatablyon either side face of the rear frame 28. The approximate centerportions of the equalizer bars 30, 30 are respectively attachedrotatably to the rear frame 28 by means of pins 29, 29.

A center arm 13 and a rear arm 15 are respectively provided rotatably onthe lower portion of the rear frame 28. The center arm 13 and the reararm 15 are also formed respectively in a V shape when observed in planview, similarly to the front arm 12.

The front end section 13A of the center arm 13 is supported rotatably inthe vertical direction on the lower front side of the rear frame 28. Apair of left and right-hand central wheels 18, 18 are installed on thetwo side faces of the rear end portion 13B of the center arm 13. Theserespective center wheels 18, 18 correspond to one example of the “firstvehicle wheels”. The upper portion of the rear end section 13B issupported on the lower side of the front end portion of the equalizerbars 30, 30, by means of springs 31, 31, which are one example of a“first suspension device”.

The front end section 15A of the rear arm 15 is supported rotatably inthe vertical direction on the lower rear side of the rear frame 28. Apair of left and right-hand rear wheels 19, 19 are installed on the twoside faces of the rear end portion 15B of the rear arm 15. These rearwheels 19, 19 correspond to one example of “second vehicle wheels”. Theupper portion of the rear end section 15B is supported on the lower sideof the rear end portion of the equalizer bars 30, by means of a rearsuspension cylinder 16, which is one example of a “second suspensiondevice”.

FIG. 3 is a side view showing a partial enlargement of an equalizer bar30. As shown in FIG. 3, stoppers 51, 51 are provided respectively oneither side face of the rear frame 28, in such a manner that theycorrespond respectively to the front end section and the rear endsection of the equalizer bars 30. The stoppers 51, 51 are provided insuch a manner that they project slightly towards the equalizer bars 30from the side face of the rear frame 28.

Furthermore, bases 52, 52 are provided respectively on the side faces ofthe equalizer bars 30 in such a manner that correspond to the stoppers51, 51. The bases 52, 52 are provided in such a manner that they projectslightly towards the equalizer bars 30. If the equalizer bar 30 isrotated through a prescribed angle or more, then the bases 52, 52 abutagainst the stoppers 51, 51, thereby preventing further rotation.

Returning to FIG. 1, a controller 47 for measuring the loaded weight isprovided in the driver's cabin 36 of the dump truck 11. The controller47 is one example of “control means”.

Furthermore, an external display lamp set 48 is provided at the base ofthe driver's cabin 36. This external display lamp set 48 serves toprovide an external display indicating the ratio of the actual loadedweight to the rated loaded weight. The external display lamp set 48 maybe constituted, for example, by a plurality of lamps 48A, 48B and 48C,each having a different color. For instance, lamp 48A is green, lamp 48Bis orange and lamp 48C is red.

The controller 47 controls the lighting up and extinguishing of thelamps 48A–48C in accordance with the weight of the cargo loaded into thevessel 21. For example, if the loaded weight is 50% or less of the ratedloaded weight, then the controller 47 does not light up any of thelamps. If the loaded weight is 50–89% of the rated loaded weight, thenthe controller 47 lights up the green lamp 48A. If the loaded weight is90–100% of the rated loaded weight, then the controller 47 lights up theorange lamp 48B. Furthermore, if the loaded weight is 100% or above ofthe rated loaded weight, then the controller 47 lights up the red lamp48C.

To take account of errors in the measurement of the loaded weight, it isalso possible to light up the orange lamp 48B if the loaded weight iswithin 90–104% of the rated loaded weight, and similarly, to light upthe red lamp 48C if the loaded weight is 105% or above of the ratedloaded weight. Furthermore, the colors of the lamps and the loadedweight categories (50% or below, 50–89%, 90–100% and 100% or above) areonly examples and may be modified in various ways.

The loading operator who is loading the cargo into the vessel 21 of thedump truck 11 observes the display on the external display lamp set 48while carrying out the loading operation. The loading operator loads thecargo into the vessel 21 in such a manner that the loaded weight becomesapproximately 100% of the rated loaded weight.

An inclination sensor 20, which is one example of “inclination angledetecting means”, is provided in the rear frame 28. This inclinationsensor 20 measures the inclination of the vehicle body in theforward/rearward direction and outputs a detection signal to thecontroller 47.

A seating sensor 46 is provided between the rear frame 28 and the vessel21. This seating sensor 46 serves to judge whether or not the vessel 21is seated on the rear frame 28. If the vessel 21 is seated on the rearframe 28, then the seating sensor 46 detects this seated state andoutputs a signal to the controller 47.

A vehicle speed sensor 49 is provided on the output shaft of thetransmission (not illustrated). This vehicle speed sensor 49 detects thenumber of revolutions of the output shaft (namely, the vehicle speed),and outputs the result to the controller 47.

A front pressure sensor 22 is provided in the front suspension cylinder14 as one example of a “second load detecting device”. This frontpressure sensor 22 detects the pressure of the oil inside the frontsuspension cylinder 14 and outputs the detected pressure to thecontroller 47.

Similarly, a rear pressure sensor 23 is provided in the rear suspensioncylinder 16 as one example of a “first load detecting device”. This rearpressure sensor 23 detects the pressure of the oil inside the rearsuspension cylinder 16 and outputs the detected pressure to thecontroller 47.

The aforementioned pressure sensors 22 and 23, the inclination sensor20, the seating sensor 46 and the vehicle speed sensor 49 arerespectively connected electrically to the controller 47. As describedhereinafter, the controller 47 is able to receive signals from therespective sensors.

FIG. 4 shows a cross-sectional diagram of a suspension cylinder. Here, afront suspension cylinder 14 is shown as an example, but a similarcomposition is also adopted for the rear suspension cylinder 16.

As shown in FIG. 4, the front suspension cylinder 14 comprises a piston38 and a cylinder 39 to which this piston 38 is attached in a slidablefashion. The piston 38 comprises, for example, a bottomedcylinder-shaped piston main body 38A and a cylinder-shaped ring member38B provided on the outer circumference of the upper portion of thepiston main body 38A.

Oil 40 is sealed inside the piston main body 38A. Nitrogen gas 41 issealed in the space between the piston 38 and the cylinder 39.

A ring-shaped cavity 42 is formed between the piston main body 38A andthe cylinder 39, in a position below the ring member 38B. A prescribednumber of first orifices 43 are provided at a prescribed position in thelongitudinal direction of the piston main body 38A, these orifices beingspaced at intervals in the circumferential direction. The first orifices43 are formed respectively in such a manner that the internal space ofthe piston main body 38A and the cavity 42 are interconnected.Furthermore, a prescribed number of second orifices 44 are providedrespectively in a different position to the first orifices 43 in thelongitudinal direction, these second orifices being spaced at intervalsin the circumferential direction. Check bores 45 are providedrespectively to the outer side of each second orifice 44.

If, for example, the front wheels 17 ride up onto a projection, or thelike, in the road surface, then the front wheels 17 are raised by theprojection and hence the piston 38 moves upwards and enters inside thecylinder 39. More specifically, the front suspension cylinder 14 iscompressed. Thereby, when the piston 38 enters inside the cylinder 39,the volume of the space formed between the upper part of the piston 38and the cylinder 39 is reduced, and hence the nitrogen gas 41 iscompressed. Furthermore, the pressure of the oil 40 sealed inside thepiston main body 38A also increases when the front suspension cylinder14 is compressed. Accordingly, the oil 40 inside the piston main body38A flows into the cavity 42 by passing through the respective firstorifices 43 and second orifices 44.

On the other hand, when the front wheels 17 have ridden over theprojection, the piston 38 moves downwards and the front suspensioncylinder 14 extends. When the piston 38 retracts inside the cylinder 39,then the pressure in the piston main body 38A declines. Since the secondorifices 44 are sealed respectively by the check bores 45, then the oil40 in the cavity 42 returns to the piston main body 38A by passingthrough the first orifices 43 only.

A pressure measurement hole 39A for measuring the pressure of thenitrogen gas 41 is formed in the upper side of the cylinder 39. One endof this pressure measurement hole 39A is connected to the space betweenthe cylinder 39 and the piston 38, and the other end thereof is openexternally on the upper side of the cylinder 39. A front pressure sensor22 is provided on this other end of the pressure measurement hole 39A.

The pressure of the nitrogen 41 sealed between the cylinder 39 and thepiston 38 is guided to the front pressure sensor 22, by means of thepressure measurement hole 39A. The front pressure sensor 22 converts thepressure of the nitrogen gas 41 into an electrical signal, which isoutput to the controller 47. By measuring the pressure of the nitrogengas 41, it is possible to measure the load (which corresponds to anexample of the “second load”) that is applied to the front suspensioncylinder 14. By this means, it is possible to determine the load appliedto the front wheel 17 to which the front suspension cylinder 14 isattached.

FIG. 5 is a block diagram showing the general composition of thecontroller 47. The controller 47 corresponds to one example of a “loadedweight measurement device for a dump truck”. The controller 47 may beconstituted by a microcomputer system.

The controller 47 may be constituted, for example, by a CPU (CentralProcessing Unit) 110, a ROM (Read Only Memory) 111, a RAM (Random AccessMemory) 112, a display drive circuit 113, a communications interface114, an input interface 115, an output interface 116, and a bus 117which interconnects these respective units.

The CPU 110 reads out and executes microprogram code stored in the ROM111. Thereby, respective processes as described below are implemented.The RAM 112 is used as a work area for temporarily storing resultsduring calculation. Furthermore, control flag information, or the like,may also be stored in the RAM 112.

The display drive circuit 113 drives a display device 47C providedinside the driver's cabin 36. Information relating to the loaded weight,and the like, may be displayed on the display device 47C, as and whenappropriate. The communications interface 114 may be provided when datacommunications are performed with a management server (not illustrated)which is disposed in a management centre, or the like. If the displaydevice 47C is not used, then the display drive circuit 113 is notnecessary. Furthermore, if the controller 47 does not conduct datacommunications, or the like, with an external device, then thecommunications interface 114 is not necessary.

The input interface 115 is a circuit for respectively receiving signalsfrom various sensors, and the like. The input interface 115 may beconnected respectively, for example, to a manual switch 47A, the seatingsensor 46, vehicle speed sensor 49, inclination sensor 20, frontpressure sensor 22, and rear pressure sensor 23. The manual switch 47Ais a switch for instructing the controller 47 to switch on a powersupply and start a calibration process, or the like, and it is providedinside the driver's cabin 36. The manual switch 47A is operated by theoperator of the dump truck 11.

The output interface 116 is a circuit for externally outputting controlsignals from the controller 47. The external display lamp set 48 and theprinter 47B, which forms one example of an external output device, areconnected to the output interface 116, for instance. The external outputdevice is not limited to the printer 47B and various types of storagedevices, such as a flexible disk device, optical disk device, hard diskdevice, semiconductor memory device, or the like, may be used. It ispossible to analyze the operating efficiency of the dump truck 11, andthe like, by recording the loaded weight measured by the controller 47,together with the measurement date and time, and the like, on arecording medium.

The composition shown in FIG. 5 is one example and the present inventionis not limited to this example. For instance, the controller 47 may alsobe constituted by a hardware circuit comprising a logical LSI (LargeScale Integration) or the like.

FIG. 6 is a block diagram focusing on the functional composition of thecontroller 47. The controller 47 may comprise, for example, acalculating section 210, a front side load detecting section 220, a rearside load detecting section 230, a measurement conditions judgingsection 240, and a storage section 250. Firstly, the peripheralfunctions of the calculating section 210 will be described, whereuponthe details of the calculating section 210 will be described.

The front side load detecting section 220 detects the load applied tothe front suspension cylinder 14 (the “second load”), on the basis ofthe detection signal from the front pressure sensor 22. Similarly, therear side load detecting section 230 detects the load applied to therear suspension cylinder 16 (the “first load”), on the basis of thedetection signal from the rear pressure sensor 23. These load detectingsections 220 and 230 may be realized by means of a CPU 110 reading inand executing a microprogram code stored in the ROM 111, for example.The load detecting sections 220 and 230 do not have to be provided inthe controller 47 and may also be provided in the pressure sensors 22and 23. More specifically, the pressure sensors 22 and 23 may also beconstituted by intelligent type pressure sensors provided with a signalprocessing LSI, or the like.

The measurement condition judging section 240 judges, for example,whether or not the start conditions for measuring the respectiveprocesses described below have been established. The measurementcondition judging section 240 judges whether or not the prescribedconditions have been established on the basis of the signals from themanual switch 47A, the seating sensor 46 and the vehicle speed sensor49, for example. One example of a prescribed condition is whether or notthe dump truck 11 has halted, for instance. The measurement conditionjudging section 240 may be realized by means of a CPU 110 reading in andexecuting a microprogram code stored in the ROM 111, for example.

The storage section 250 is realized by a RAM 112, for example. Thestorage section 250 can store, for example, the loaded weight calculatedby the calculating section 210, the initial load in an empty state,control information, and the like.

The calculating section 210 performs calculation processes. Thecalculating section 210 may comprise, for example, a front side loadvertical component calculating section 211, a total load verticalcomponent calculating section 212, a total load calculating section 213,and an overall load calculating section 214.

The front side load vertical component calculating section 211calculates the vertical component of the front side load on the basis ofthe front side load detected by the front side load calculating section220 and the angle of inclination of the vehicle body detected by theinclination sensor 20.

The front side load vertical component calculating section 211constitutes one example of a “vertical component calculating section”,in conjunction with the total load vertical component calculatingsection 212.

The total load calculating section 213 calculates the total load appliedto the springs 31 and the rear suspension cylinder 16 on the basis ofthe rear side load detected by the rear side load detecting section 230and the mechanical settings of the equalizer bars 30 and the like. Inother words, it calculates the total of the loads applied respectivelyto the central wheels 18 and the rear wheels 19.

As described further hereinafter, if the central wheels 18 and the rearwheels 19 are balanced by the equalizer bars 30, as shown in FIG. 3,then the moment at the central wheels 18 (the center moment) and themoment at the rear wheels 19 (the rear moment) are equal. The centermoment is derived from the product of the center load F1 and thedistance D1 from the pin 29 to the spring 31 (F1·D1). The rear moment isderived from the product of the rear load F2 and the distance D2 fromthe pin 29 to the center of the rear suspension cylinder 16 (F2·D2).

Therefore, since (F1·D1)=(F2·D2), the equation F1=(F2·D2)/D1 can beobtained. As this equation shows, the center load F1 can be determinedfrom the rear load F2, and the set mechanical values of the equalizerbar 30 (D1 and D2), only. By performing a calculation of this kind, thetotal load calculating section 213 is able to calculate the total valueof the loads applied to the center and rear sides.

The total load vertical component calculating section 212 calculates thevertical component of the total load on the basis of the total loaddetected by the total load calculating section 213 and the angle ofinclination of the vehicle body detected by the inclination sensor 20.

The overall load calculating section 214 calculates the overall load byadding together the calculation results of the front wide load verticalcomponent calculating section 211 and the total load vertical componentcalculating section 212. The overall load calculated in an empty stateis taken as the initial load. By subtracting the initial load from theoverall load calculated when the vehicle is in a loaded state, it ispossible to determine the current loaded weight.

The lighting up of the external display lamp set 48 is controlled on thebasis of the loaded weight calculated by the overall load calculatingsection 214. Furthermore, the loaded weight thus calculated is stored inthe storage section 250 and printed on the printer 47B. Moreover, forexample, information such as the calculated loaded weight, themeasurement date and time, and identification information for the dumptruck 11, may also be transmitted to an external management device, bymeans of the communications interface 114.

Below, a sequence for measuring the loaded weight will be described.When detecting the loaded weight, firstly, all of the loads applied tothe front wheels 17, the central wheels 18 and the rear wheels 19 aremeasured, when the vehicle is in an empty state with no cargo loaded inthe vessel 21. In other words, the initial load prior to loading ismeasured. In the present specification, this measurement of the initialload is called “calibration”. The initial load when the vessel 21 isempty, is the unsprung weight of the dump truck 11 in an empty state.This initial load may also be called “empty load”. After measuring theinitial load, the overall load when the cargo has been loaded into thevessel 21 is measured, and by subtracting the initial load from thisoverall load, the loaded weight of cargo is calculated.

FIG. 7 is a flowchart showing an overview of calibration processing. Ofthe suspension cylinders and pressure sensors provided respectively onthe left and right-hand sides of the vehicle, the following descriptionrelates to the suspension cylinder and pressure sensor provided on oneside, but in practice, similar calculations are carried out for theother side as well, and the average of the values acquired on the leftand right-hand side is obtained. Furthermore, here “step” is abbreviatedto “S”.

When performing a calibration process, the dump truck 11, with thevessel 21 in an empty state, is caused to travel in a straight line overa relatively flat terrain at a prescribed approximately uniform speed,for a prescribed time period t1 (for example, 30 seconds). This iscalled “calibration travel”. Therefore, in this process, it is firstjudged whether or not calibration travel has started (S10). The judgmentof whether or not calibration travel has started can be made on thebasis of a signal from the vehicle speed sensor 49 and the seatingsensor 46, for example.

If calibration travel has started (S10: YES), then the controller 47starts a timer for measuring the prescribed time period t1 (S1).

Furthermore, the controller 47 detects the load applied to the frontsuspension cylinder 14 on the basis of the signal from the frontpressure sensor 22 provided in the front suspension cylinder 14 (S12).The load applied to the front suspension cylinder 14 which is detectedat S12 is called the “front side load”.

Next, the controller 47 detects the load applied to the rear suspensioncylinder 16 (hereafter, called the “rear load”) on the basis of thesignal from the rear pressure sensor 23 provided in the rear suspensioncylinder 16 (S13).

The controller 47 multiplies the detected rear load by two (S14). Inthis way, the sum of the rear load and the load applied to the spring 31(hereafter, called the “center load”) is determined. This sum is calledthe “total load”.

Here, step S14 will be described in more detail. As shown in FIG. 3, thecentral wheel 18 and the rear wheel 19 are supported on either end of arotatable equalizer bar 30, by means of the spring 31 and the rearsuspension cylinder 16. If the rotatable equalizer bar 30 is notrotated, then the moment applied to the front end of the equalizer bar30 is equal to the moment applied to the rear end of the equalizer bar30.

In other words, as described previously, the product of the center loadF1 and the distance D1 from the pin 29 to the center of the spring 31(namely, F1·D1) is equal to the product of the center load F2 and thedistance D2 from the pin 29 to the center of the rear suspensioncylinder 16 (namely, F2·D2). Therefore, it is possible to obtain theequation F1=(F2·D2)/D1, as stated previously. It can be seen that thecentral load F1 can be derived from this equation by multiplying therear side load F2 by (1+D2/D1), (namely, F1=F2×(1+D2/D1)).

In the present embodiment, a pin 29 is provided in approximately thecentral portion of the equalizer bar 30, and the values of D1 and D2 areapproximately the same (D1=D2). Since the respective distances from thepin 29 forming the fulcrum point are equal, then the rear load F2 isapproximately equal to the central load F1 (F1=F2). Consequently, it ispossible to determine the total load (F1+F2) simply by multiplying therear load F2 by two.

Next, the controller 47 detects the angle of inclination of the dumptruck 11 in the forward/rearward direction, on the basis of the signalfrom the inclination sensor 20 (S15). The controller 47 corrects thefront side load, and the total of the central load and the rear load, torespective vertical component loads on the basis of the angle ofinclination (S16). By this means, a corrected value for the front sideload applied to the front wheels 17 and a corrected value for the totalload applied to the central wheels 18 and the rear wheels 19 arederived.

The controller 47 calculates an overall load value by adding togetherthe corrected value of the front load and the corrected value of thetotal load (S17). The controller 47 stores this overall load value inthe storage section 250 and it repeats steps S12 to S17 until theprescribed time period t1 has passed (S18).

When the prescribed time period has passed (S18: YES), the controller 47finds the average of the plurality of overall load values stored in thestorage section 250 (S19). This average is taken as the initial load ofthe dump truck 11. The controller 47 stores the initial load thuscalculated in the storage section 250 and then terminates thisprocessing sequence.

FIG. 8 is a flowchart showing an overview of a process for measuring theloaded weight when cargo has been loaded into the vessel 21. Thisprocess can be performed by a sequence that is substantially the same asthat in S10–S19 shown in FIG. 7.

Firstly, the controller 47 judges whether or not a loaded weightmeasurement process has started (S10A). For example, if the manualswitch 47A includes a “measurement start switch”, then the loaded weightmeasurement process is started when the operator activates this switch(S10A: YES).

Here, for example, the start date and time of the loaded weightmeasurement process is compared with the registration date and time ofthe initial load stored in the storage section 250. If a prescribedperiod of time or more has passed since the registration date and timeof the initial load, then it is possible to prompt the operator to carryout new registration of the initial load, via the external display lampset 48 or the display device 47C. Alternatively, when outputting ameasurement result from the loaded weight measurement process, it ispossible to output the initial load value used as a basis for themeasurement, and the date and time of registration of that initialvalue, together with the result.

When a measurement process is started, the controller 47 starts a timerfor measuring a second prescribed time period t2 (S11A). This timer t2is used in order to measure the loaded weight a plurality of times.

Similarly to the calibration process described above, the controller 47detects the front side load and the rear side load (S12A, S13A), andderives a total load by multiplying the rear load by two (S14A). Thecontroller 47 then detects the angle of inclination (S15A), andrespectively corrects the front side load and the total load on thebasis of the angle of inclination (S16A).

The controller 47 calculates the overall load by adding together thevertical component of the front side load and the vertical component ofthe total load (S17A). The controller 47 stores the calculated overallload value in the storage section 250 and it repeats steps S12A to S17Auntil the prescribed time period t2 has passed (S18A).

When the prescribed time period t2 has elapsed (S18A: YES), thecontroller 47 finds the average of the plurality of overall loads storedin the storage section 250 and then calculates the loaded weight bysubtracting the initial load from this average value (S19A).

According to the present embodiment as described above, the centralwheel 18 is supported on the equalizer bar 30 by means of a spring 31and the rear wheel 19 is supported on the equalizer bar 30 by means of arear suspension cylinder 16.

Therefore, the rear load is determined by a rear pressure sensor 23provided in the rear suspension cylinder 16, and the total of thecentral load and the rear load is found by multiplying the rear load bytwo. In the present embodiment, it is sufficient only to measure therear load directly, and there is no need to measure the load applied tothe spring 31 supporting the central wheel 18. Consequently, it is notnecessary to provide a sensor for detecting the amount of extension orcontraction of the spring 31.

Furthermore, in the present embodiment, even if the spring 31 isreplaced with a suspension cylinder for the purpose of supporting thecentral wheels 18, it is not necessary to provide a pressure sensor inorder to determine the load applied to the suspension cylinder.

In this way, according to the present embodiment, it is possible tomeasure the loaded weight accurately by means of a small number ofsensors, and hence loaded weight measurement performance for the dumptruck 11 can be improved without significantly increasing manufacturingcosts.

With the passage of time, the oil 40 inside the suspension cylinders 14and 16 decreases, and hence variation in the output of the pressuresensors 22 and 23 can be expected. In order to correct this variation,it is desirable that the initial load be measured by performingcalibration at periodic intervals.

Second Embodiment

Next, a second embodiment will be described on the basis of FIG. 9–FIG.11. In this embodiment, as described below, it is previously judgedwhether or not conditions for accurately measuring the loaded weighthave been established, and if accurate measurement cannot be performed,then a cautionary warning is issued to the operator, or the like.Furthermore, in this embodiment, automatic diagnosis is carried out onthe basis of the loaded weight of the dump truck 11, in order to tellwhether or not the truck is situated in an accurate measurementenvironment.

Firstly, a general work procedure of the dump truck 11 will bedescribed. FIG. 9 shows a work procedure of the dump truck 11. The dumptruck 11 halts at a loading point, with the empty vessel 21 seated onthe rear frame 28 (S21). The loading operator loads a cargo to beconveyed, such as sand, into the vessel 21, by means of a hydraulicshovel, wheel loader, or the like (S22).

When the loaded weight G has become equal to or greater than aprescribed value GM (S23: YES), the dump truck 11 starts to travel andtransports the cargo to a prescribed unloading point (S24). Uponarriving at the unloading point, the dump truck 11 moves the vessel 21to the “tipped up” position, thereby unloading the cargo (S25).

When unloading has completed, the dump truck 11 moves the empty vessel21 to the “tipped down” position, returns to the loading point andstarts loading again (S26).

This sequence of steps S21–S25 is taken as one work cycle, and the dumptruck 11 repeats this work cycle a plurality of times.

In a work cycle of this kind, at S21, if the dump truck 11 has halted ata loading point, then either the central wheels 18 or the rear wheels 19may be raised up on a projection such as a rock projecting upwards fromthe surface at the loading point, or they may have fallen into adepression in the surface.

If the projection or the depression is large in size, then the equalizerbar 30 will be inclined significantly, and as shown in FIG. 10, the base52 will make contact with the stopper 51 and further rotation of theequalizer bar 30 will be prevented. Below, this state is called a statewhere the equalizer bar 30 is abutted against the stopper 51.

In a state where the equalizer bar 30 is abutted against the stopper 51,the equalizer bar 30 becomes unable to rotate, and hence the frontmoment applied to the front end portion of the equalizer bar 30 and therear moment applied to the rear end portion of the equalizer bar 30 arenot necessarily equal.

Therefore, the premise that “the central side load F1 is equal to therear side load F2 multiplied by (1+D2/D1) (namely, F1=F2×(1+D2/D1))” isnot established, and therefore it is not possible to calculate the totalload accurately.

In order to avoid this, in the present embodiment, it is previouslyjudged whether or not the equalizer bar 30 is abutting against thestopper 51, on the basis of the loaded weight when the dump truck 11 ishalted in an empty state. If the equalizer bar 30 is abutting againstthe stopper 51, then this fact is reported to the operator of the dumptruck 11, thus notifying the operator that the halt position of the dumptruck 11 is unsuitable and prompting the operator to move the dump truck11.

A more detailed description is given below. FIG. 11 is a flowchartshowing an overview of a process for judging whether or not the haltposition of a dump truck 11 is suitable.

Firstly, the controller 47 judges whether or not the dump truck 11 whichhas returned to the loading point has halted, on the basis of the signalfrom the vehicle speed sensor 49 (S31).

If it is judged that he dump truck 11 has halted (S31: YES), then thecontroller 47 detects the loaded weight G in accordance with theprocedure S12–S17 described above (S32). In this case, the loaded weightG is measured during a prescribed time period and the average valuethereof is found.

The controller 47 judges whether or not the loaded weight G thusmeasured is in a prescribed range (−G1≦G≦G2) (S33). Here, −G1 and G2 arevalues set on either side of 0, and if G is restricted within thisrange, then the loaded weight G can be judged to be substantially zero.This point is described further below.

If the loaded weight G is restricted within this prescribed range in thevicinity of zero (S33: YES), then the controller 47 judges that the haltposition of the dump truck 11 is suitable (S34). The controller 47 thenreports the fact that the halt position of the dump truck 11 issuitable, to the truck operator and loading operator (S35). The truckoperator or loading operator confirms this report and then starts aloading operation (S36).

The report made in S35 may be varied according to the recipient. Forexample, a report can be made to the operator in the driver's cabin 36,by displaying a message, such as “halt position suitable”, on thedisplay device 47C. A report can be made to a loading operator situatedoutside the dump truck 11 by means of the external display lamp set 48.More specifically, for example, even if a prescribed time period (forexample, approximately several seconds) has elapsed after the dump truck11 halted, then this can be reported by extinguishing the externaldisplay lamp set 48, or the like.

Alternatively, it is also possible to report the fact that the haltposition of the dump truck 11 is suitable by consecutively lighting upthe green lamp 48A and the red lamp 48C in the external display lamp set48, for example, or causing same to flash, for a prescribed short periodof time. Moreover, it is also possible to provide a special lamp inorder to report that the halt position is suitable. Furthermore, areport may also be provided by a synthesized voice and a buzzer sound,instead of or in conjunction with the lamps.

Conversely, if the loaded weight G has moved outside the prescribedrange in the vicinity of zero (S33: NO), then the controller 47 judgesthat the halt position of the dump truck 11 is unsuitable (S37). Thecontroller 47 then reports the fact that the halt position of the dumptruck 11 is unsuitable, respectively, to the truck operator andunloading operator (S38).

Similarly to the foregoing description, this report may be changed inaccordance with the position of the recipient (namely, if the recipientis situated inside or outside the dump truck 11). For example, a reportmay be made to the operator by displaying a flashing message, such as“halt position unsuitable”, on the display device 47C, or by sounding abuzzer, or the like. A report may be made to the loading operator, forexample, by causing all of the lamps 48A–48C in the external displaylamp set 48 to flash.

If a report has been issued indicating that the halt position isunsuitable, then the loading operator waits without carrying outloading. Upon receiving this report, the truck operator moves the dumptruck 11 to a flatter position (S39).

When the dump truck 11 has moved and halted, the process from S31onwards is implemented again. Thereby, if it is judged that the haltposition of the dump truck 11 is suitable (S33: YES), then a loadingoperation into the vessel 21 is started (S36).

The step S33 is now described in detail. If the equalizer bar 30 is notin an abutted state against the stopper 51, more specifically, if thedump truck 11 has been halted in a relatively flat position and the freerotation of the equalizer bar 30 is not limited, then the rear load F2and the central load F1 will be approximately equal in step S33.

Therefore, as described above, by multiplying the rear load F2 by(1+D2/D1), it is possible to determine the central load F1, and hencethe total load of the rear load F2 and the central load F1 (F1+F2) canbe calculated. As described previously, in the present embodiment, sinceD1=D2, the total load can be determined simply by multiplying the rearload by two.

Here, at S33, since the loaded weight G is measured when the vessel 21is empty, then provided that the halt position of the dump truck 11 issuitable, the overall value of the load after correction on the basis ofthe detection signal from the inclination sensor 20 (S19A) will be equalto the initial load. Therefore, the loaded weight will be approximatelyzero.

However, if the equalizer bar 30 is abutting against the stopper 51,then since the free rotation of the equalizer bar 30 is restricted, therear load F2 and the central load F1 will not be equal, but rather, onewill be greater than the other. Taking an extreme example, in asituation where the central wheels 18 are suspended in the air and therear portion of the vehicle body 25 is supported by the rear wheels 19only, the central load F1 will be approximately zero, and the rear loadF2 will be double the load in a case where the dump truck 11 is haltedin a suitable position.

Therefore, if free rotation is halted by the equalizer bar 30 abuttingagainst the stopper 51, then it is not possible to calculate the totalload accurately on the basis of the rear load F2 and hence a large erroris produced in the measurement of the loaded weight.

At S33, since the loaded weight G is measured when the truck is empty,if the halt position (vehicle position) of the dump truck 11 is notsuitable, then the loaded weight G will not assume a value in thevicinity of zero, but rather, it will substantially depart from theregion of zero.

Therefore, at S33, if the loaded weight G does not lie within theprescribed range in the vicinity of zero (S33: NO), then it is judgedthat the halt position of the dump truck 11 is unsuitable. The lowerlimit G1 and the upper limit G2 which substantially limit the range ofzero may be the same value or they may be different values.

Rather than judging whether or not the halt position of the dump truck11 is suitable on the basis of the loaded weight G, it is also possibleto make this judgment on the basis of the rear side load, for example.More specifically, a rear side load in an empty state is previouslydetected and stored, and the rear side load detected at step S33 iscompared with this value. If the two values are substantially equal, orif the difference between these values is substantially zero, then itcan be judged that the halt position of the dump truck 11 is suitable.Conversely, if the two values are different, or if the differencebetween the values exceeds a range of substantially zero, then it can bejudged that the halt position of the dump truck 11 is unsuitable.

Alternatively, it is possible to judge whether or not the halt positionof the dump truck 11 is suitable on the basis of the vertical componentof the rear load or the total load.

According to the present embodiment as described above, it is previouslyjudged whether or not the loaded weight can be measured accurately,before the loading operation, and if accurate measurement cannot beachieved, then this fact is reported respectively to the truck operatorand loading operator situated inside and outside the dump truck 11.Thereby, since the loading operation can be started after the dump truck11 has been halted in a suitable position, then it is possible tomeasure the loaded weight accurately.

Third Embodiment

Next, a third embodiment will be described on the basis of FIG. 12–FIG.14. In this embodiment, as described hereinafter, a limit switch 50 isused in order to detect whether or not the equalizer bar 30 is abuttedagainst the stopper 51.

In the second embodiment described above, it is judged whether or notthe equalizer bar 30 is abutting against the stopper 51 when the dumptruck 11 is halted in an empty state. However, the equalizer bar 30 mayalso become abutted against a stopper 51 in other circumstances, forinstance, during loading, during travel or during unloading, and notonly when the dump truck 11 is halted in an empty state. In thesecircumstances also, it is possible that error may occur in themeasurement values for the loaded weight due to similar reasons to thosedescribed above.

In this embodiment, limit switches 50 are provided in order to detectwhether or not the equalizer bar 30 is abutted against a stopper 51, asshown in FIG. 12. The limit switches 50 may be provided on the side ofrespective stoppers 51, for example. Alternatively, limit switches 50may be provided respectively on bases 52.

The limit switch 50 may be constituted by a mechanical type limit switchin which an internal switch is actuated by the extension or contractionof a plunger, for example. Alternatively, for example, it may also beconstituted by a proximity switch which detects the proximity of aphysical body on the basis of change in a high-frequency magnetic field.Moreover, it is also possible to use a reflective type opto-electricalswitch as the limit switch, for example. Furthermore, instead of thelimit switch 50, a distortion gauge may be attached to at least one ofthe stopper 51 and the equalizer bar 30, and abutting may be detected onthe basis of the signal from the distortion gauge.

In the following description, “abut” represents both a case where thebase 52 of the equalizer bar 30 makes contact with a stopper 51 and acase where it approaches same to a position of near contact.

As shown in the block diagram in FIG. 13, the signal from the limitswitch 50 is input to the controller 47.

FIG. 14 is a general flowchart of an abutment judgment process using asignal from a limit switch 50. The controller 47 monitors whether or notthe equalizer bar 30 has abutted against a stopper 51, on the basis ofsignals from the limit switches 50 (S41). For example, the controller 47is able to check the signal level of the limit switches 50 at prescribedshort time periods. Alternatively, it is also possible to connect thesignals from the limit switches 50 to an interrupt input terminal of thecontroller 47, an abutted state being detected by generation of aninterrupt input.

If abutment of the equalizer bar 30 against a stopper 51 is detected bya limit switch 50 (S41: YES), then the controller 47 sets the abutmentjudgment flag to “1” (S42). This abutment judgment flag is stored in thestorage section 250, and the various processes executed by thecontroller 47 reference this abutment judgment flag, either compulsorilyor according to requirements. Alternatively, it is possible to omit theabutment judgment flag and to send an interrupt immediately to theprograms being executed, when an abutted state between the equalizer bar30 and the stopper 51 is detected.

The controller 47 reports to the operator that the equalizer bar 30 hasabutted against the stopper 51 by displaying a prescribed warningmessage on the display device 47C, or by sounding a buzzer, for example.Furthermore, the controller 47 may issue a report to an externallysituated loading operator, via the external display lamp set 48.

If the measured value of the loaded weight is displayed on the displaydevice 47C, then the controller 47 is also able to display the fact thatthe equalizer bar 30 and the stopper 51 are abutting. For example,values for the loaded weight measured when these members are in anabutted state can be displayed in a red color or in a flashing manner,or the like, and hence it is possible readily to distinguish thesevalues from other measurement values which were measured in a normalstate.

Furthermore, if the measurement values for the loaded weight are outputfrom the printer 47B, then the controller 47 may cause particular textor a particular symbol (for example, a “*” symbol) to be printedalongside loaded weight measurement values which were measured when theequalizer bar 30 and the stopper 51 were in an abutted state. In thecase of a color printer, it is also possible to print measurement valuesthat were measured in an abutted state, in a red color, or the like.

If the loaded weight is measured a plurality of times and an averagevalue is determined, then the controller 47 is also able to excludevalues measured when the equalizer bar 30 and the stopper 51 were in anabutted state, in such a manner that these values are not used in theprocess of calculating the average value. Alternatively, if an averagevalue is calculated by using values that were measured in an abuttedstate and which have a possibility of containing measurement error, thenthe controller 47 is able to output information indicating thereliability of the average value (for example, text or a symbol such as“#”) in association with the average value.

In this way, in the present embodiment, since a limit switch 50 isprovided for detecting whether or not the equalizer bar 30 and thestopper 51 are in an abutted state, it is possible readily to judgewhether or not accurate measurement of the loaded weight is possible,not only when the dump truck 11 is halted in an empty state, but alsoduring loading into the vessel 21, during travel of the dump truck 11,and during unloading of the cargo from the vessel 21. Thereforeoperability is improved. More specifically, it is possible readily todistinguish the reliability of the measurement loaded weight values,even while the dump truck 11 is in various different modes (empty haltedmode, loading mode, transporting mode, or unloading mode).

The present invention is not limited to the embodiments described above.A person skilled in the art may be able to make various additions andmodifications within the scope of the present invention. For example, acase is described where one pressure sensor is provided respectively ineach suspension cylinder, but the present invention is not limited tothis and it is also possible to provide a plurality of pressure sensorsrespectively in each suspension cylinder.

Moreover, an example was given in which the central wheels are supportedby springs and the rear wheels are supported by rear suspensioncylinders, but the present invention may also be applied to a converseconfiguration in which the central wheels are supported by suspensioncylinders and the rear wheels are supported by springs. Furthermore, acomposition may be adopted in which both the central wheels and the rearwheels are supported respectively by suspension cylinders.

An articulated type dump truck was described as an example, but thepresent invention is not limited to this and may also be applied to adump truck having a plurality of wheels supported by equalizer bars.

Furthermore, the present invention is not limited to a configurationwhere the central wheels and the rear wheels are coupled by equalizerbars, and it may also be applied to a configuration where the frontwheels and the central wheels are coupled by equalizer bars. Moreover,the present invention may also be applied to a dump truck having aplurality of wheels coupled respectively by equalizer bars, in thefront/rear direction of the vehicle.

1. A loaded weight measurement method for a dump truck comprising a setof equalizer bars respectively provided rotatably on the left andright-hand sides of a vehicle body; first vehicle wheels supportedrespectively by means of first suspension devices on one side of eachequalizer bar; second vehicle wheels supported respectively by means ofsecond suspension devices on the other side of each equalizer bar; andthird vehicle wheels provided respectively on the left and right-handsides of said vehicle body separately from said equalizer bars, andbeing supported respectively by means of third suspension devices, theloaded weight measurement method comprising: a first step of detecting afirst load applied to either said first suspension device or said secondsuspension device; a second step of detecting a second load applied tosaid third suspension device; a third step of detecting an angle ofinclination of said vehicle body; and a fourth step of calculating aloaded weight on the basis of said first and second loads detectedrespectively in said first and second steps, and said angle ofinclination detected in said third step.
 2. The loaded weightmeasurement method for a dump truck according to claim 1, wherein saidfourth step comprises: a first sub-step of calculating a total loadapplied to said first and second suspension devices on the basis of theratio between the respective distances from a center of rotation of atleast one of said equalizer bars to said first and second suspensiondevices, and said first load detected in said first step; a secondsub-step of respectively calculating a vertical load from said totalload calculated in said first sub-step and said second load detected insaid second step, on the basis of said angle of inclination detected insaid third step; and a third sub-step of calculating said loaded weightby adding together a vertical component of said first load and avertical component of said second load calculated in said secondsub-step.
 3. The loaded weight measurement method for a dump truckaccording to claim 1, wherein a judgment step for judging whether or notthe equalizer bars are in a state of free rotation is executed prior tosaid first step, respective steps following said first step are executedif it is judged in said judgment step that said equalizer bars are in astate of free rotation, and a notification is reported if it is judgedin said judgment step that said equalizer bars are not in a state offree rotation.
 4. The loaded weight measurement method for a dump truckaccording to claim 3, wherein said judgment step judges whether or notsaid equalizer bars are in a state of free rotation on the basis of adetection signal from abutment detecting means for detecting an abuttedstate of said equalizer bars and said vehicle body.
 5. The loaded weightmeasurement method for a dump truck according to claim 3, wherein saidjudgment step judges whether or not said equalizer bars are in saidstate of free rotation, by comparing at least one of said first loaddetected in an empty state in said first step and said loaded weightcalculated in an empty state in said fourth step, with a previouslyestablished prescribed value for an empty state.